There are many kinds of power rotary tools such as an electric power drill, a battery drill, a hammer drill, a vibratory drill, an electric power driver or the like.
The electric power drill and the battery drill are used to perform boring work for iron plate or the like and boring work for woody material.
Also, the hammer drill and the vibratory drill are used to perform boring work while imparting vibrations to stone material or the like by a built-in vibration generating mechanism or the like. The electric power driver is used to perform screwing work for a board or the like by a built-in clutch.
The present invention relates to a chuck device for gripping a tool, used for mounting a tool (such as a drill bit and a driver bit) for rendering the tool to perform the above-described various works.
In a chuck device having a structure for gripping a tool only by a manual operation without any tool, in order to generate a large tool gripping force with a small torque (torque obtained by manual rotation), and in order to keep a smooth rotation of a rotary nut engaged with claws even if a fastening reactive force in a thrust direction is applied to the rotary nut, balls (steel balls) are interposed between a back surface of the rotary nut and a flange extending from a chuck body.
In such a chuck device having the structure for gripping the tool only by the manual operation without any tool, since the balls are arranged for the above-described reason, the rotary nut is smoothly rotated but this means that the screwed and fastened rotary nut is likely to be loosened.
Therefore, so far, there has been proposed a chuck device having a structure provided with a means for preventing the loosening of the rotary nut, in particular, a chuck device for preventing the grip of the tool is prevented from being loosened due to the vibrations or the like when the work is carried out by using an electric rotary power tool incorporating the vibration generation mechanism, an electric rotary power tool incorporating a shock generating mechanism or an electric rotary power tool incorporating a clutch mechanism.
In, for example, U.S. Pat. No. 5,145,194 (hereinafter referred to as a prior art example), recess portions are provided in the rolling surface per se of the balls, a resistance is imparted to exhibit the loosening preventing effect by the resistance when the balls that are present in the recess portions are disengaged from the recess portion while rotating (orbiting while rotating about their own axes).
However, in the prior art, the recess portions are formed in the rolling surface, when the fastening reactive force is applied in the thrust direction to the balls, the balls are not rotated smoothly. This means that it is impossible to obtain a large tool gripping force for the chuck device for holding the tool only by the manual operation without using any tool and would become fatal (To prevent the loosening while sacrificing the maintenance of the large tool gripping force is completely opposed to the inherent purpose.) In the case where the balls are present on a border between the recess portions and the flat surfaces therearound, i.e., at the ridge positions, the fastening reactive force is applied in the thrust direction without any change so that a large surface pressure is applied to the ridge line, resulting in deformation of the ridge line. This damages the ridge lines of the recess portions due to the repeated use, resulting in the degradation of the loosening prevention effect.